334 T. Venkatesan and S. K. Jalali
including the quality and fitness of the parasitoid
and complex interactions between the parasitoid,
the target pest, the crop and environmental con-
ditions. Considering the present scenario of very
low levels of parasitism achieved during hotter
months (35–40 °C, parasitism ≤ 25 %), it is abso-
lutely necessary to go for the parasitoids that are
field collected to high-temperature conditions.
Hence, high-temperature field-collected popula-
tion of T. chilonis will survive better in hostile
crop environment and control lepidopteran pests
efficiently.
The efficacy of trichogrammatids is largely
dependent on temperature conditions. Earlier
studies have suggested that temperature > 35 °C
prevents adult emergence (López and Morrison
1980 ; Singh and Jalali 1994 ; Scholler and Hassan
2001 ), thereby reducing efficacy of trichogram-
matids drastically at higher temperature. Scott
et al. ( 1997 ) examined the consequences of accli-
mation for survival and the fitness components of
T. carverae and reported that acclimating wasps
by rearing at constant temperature influenced
parasitism rates at those temperature. They also
observed that heat hardening at 33 °C during de-
velopment also resulted in significant increases
in survivorship of adults after exposure to 40 °C.
Thomson et al. ( 2001 ) reported that heat harden-
ing is a well known form of acclimatization in
many invertebrates where exposure to high but
sublethal temperature protects against subsequent
heat induced death and heat hardening enhanced
adult fitness in the field under hot conditions.
Carrière and Boivin ( 2001 ) reported that selec-
tion of Trichogramma lines for improvement of
parasitism at constant low, medium, or high tem-
perature indicated that a change in performance
at one temperature concurrently resulted in oppo-
site changes at distant temperature. Thus, genetic
trade-off in performance at different temperature
and phenotypic plasticity in maternal selection
may constrain evolution of the thermal niche in
Trichogramma.
The efficacy of trichogrammatids is largely
dependent on temperature conditions. Singh and
Jalali ( 1994 ) found that the temperature > 35 °C
affects emergence, thereby reducing efficacy
of trichogrammatids drastically. Abraham and
Pradhan ( 1976 ) made an attempt to select strain
of T. chilonis for tolerance to high temperature
(32–35 °C) from heterogeneous populations
of the parasitoids developed by interbreeding
strains from Ambajipet (Andhra Pradesh). Cud-
dalore (Tamilnadu), Delhi, Lucknow, Ludhiana,
and Mandya (Karnataka) but were unsuccessful.
Ludhiana, Delhi, and Ambajiper strains, how-
ever, were more tolerant to high temperature
and low humidity. Significant improvements in
adult emergence, fecundity, and progeny produc-
tion were made after rearing Ludhiana and Delhi
strains for 32–33 generations at progressively
increasing temperature from 30 to 33 °C and de-
creasing humidity from 60 to 10 %.Development of T. chilonis Population
with Multiple Insecticide and
Temperature Tolerance
The results on the development process of a
population of T. chilonis field-collected to three
insecticides and high temperature revealed that
percent mortality ranged from 94.0 to 100.0 %
during 1st exposure. In endosulfan treatment,
mortality remained > 80.0 % for 36 generations
after 6 h of constant exposure. In F 45 generation,
mortality recorded was 80.0 %. The concentra-
tion was increased to double the field recom-
mended dosages, that is, 4.0 ml/L. Increasing
concentration increased the mortality to 95.0 %
and after constant selection for 10 generations
mortality declined to 70.0 % and remained so
throughout the period of development. The mor-
tality declined due to constant exposure in each
generation to the insecticides and high tempera-
ture, thus indicating that adaptation to conditions
can induce tolerance in the parasitoid.
In monocrotophos treatment, mortality was
100.0 % in 1st generation in high temperature and
sprayed situation after 6 h of constant exposure.
The higher mortality obtained in monocrotophos
indicated that this insecticide was more toxic
than other insecticides. The mortality declined
due to constant exposure after 45th generation
and it was 80.0 %. The increase in concentration
to double the field recommended dosages, that